If memory is what defines personal identity, then the psychological coping mechanism labelled multiple personality disorder makes good sense. As I understand it, as a person experiences emotional trauma, he or she locks off the memories and blocks their accessibility from normal brain function, creating a new person to handle the strain. If (and I don't know if this is how it works or not) walling off pockets of memories can divide a person's consciousness into noticeably different personalities, doesn't that support the memory theory? Maybe I don't understand things very well, but that seems to make sense to me. The problem, then, is figuring out whether all the "personalities" are "persons," or if they are merely different aspects of one "person." Maybe.